1. Field of the Invention
The present invention relates to a decompression container, such as a treatment container and a vacuum reserve chamber, of which a top plate and a side wall produce no dust despite repeated decompression.
2. Information of the Related Art
Treatment containers of various treatment apparatuses, such as film forming apparatuses, etching apparatuses, etc., which are used in a semiconductor device manufacturing process, are closed airtightly so that a treatment chamber therein can be decompressed to a predetermined degree of vacuum, e.g., 10.sup.-6 to 10.sup.-7 torr. After a semiconductor wafer (hereinafter referred to simply as wafer) for use as an object to be treated is placed on, for example, a mount in the treatment chamber, it is subjected to a predetermined treatment under a reduced pressure in each apparatus.
In order to shorten the decompression time to improve the throughput or prevent involvement of dust from the atmosphere, many of the treatment containers are coupled with a vacuum reserve chamber called a load locking chamber by means of a gate valve. The reserve chamber is adjusted to a degree of vacuum (e.g., 10.sup.-2 torr) lower than that of the treatment container. After the to-be-treated object is temporarily delivered into the vacuum reserve chamber, it is carried into the treatment chamber when the two chambers are equalized in the degree of vacuum.
Thus, the treatment container or the vacuum reserve chamber is evacuated to a predetermined degree of decompression. Accordingly, junctions between a top plate, side plate, and bottom plate of the container or chamber require a high degree of airtightness. One such junction of a conventional decompression container of this type is constructed in the manner shown in FIG. 11, for example.
FIG. 11 shows the way a top plate 101, which is formed of an aluminum plate material treated with anodized aluminum, and a side wall 102 of the same material are joined together. A groove 103 is formed in the upper end face of the side wall 102, and an O-ring 104 for use as a seal member is fitted in the groove 103 so that its top portion projects from the groove. The upper end face of the side wall 102 is joined close to the lower surface of the peripheral edge portion of the top plate 101, and a clamping member 105 such as a bolt, which is located outside the O-ring 104, is screwed into the upper end face of the side wall 102 from above the top plate 102. Thus, the top plate 101 and the side wall 102 are coupled together.
As mentioned before, the treatment container of this type is evacuated to a high degree of vacuum, e.g., 10.sup.-6 to 10.sup.-7 torr or 10.sup.-2 torr. When the container is decompressed, therefore, the top plate 101, for example, is subjected to a very high pressure attributable to atmospheric pressure, as indicated by the arrow in FIG. 11. Thus, even in the case of a conventional treatment container of the same aluminum material for wafer treatment, the top plate 101 is bound to bend downward. In the case of a top plate with a radius of about 300 mm and a thickness of 30 mm, for example, a maximum deflection d in its central portion attains more than 0.25 mm. In this case, the starting point of deflection lies on an inner corner edge portion 102a of the side wall 102.
As mentioned before, moreover, the treatment container or the vacuum reserve chamber is repeatedly decompressed or restored with every treatment of the to-be-treated object. In a sheet treatment apparatus which pursues a particularly high throughput, the decompression and restoration are repeated many times an hour, depending on the type of the treatment. The top plate 101 bends in the manner shown in FIG. 12 with every decompression. Thus, when the top plate 101 is restored to its original state, the deflection is reduced. In the case of the vacuum reserve chamber, in particular, the top plate 101 is brought to a horizontal state, as shown in FIG. 11, when exposed to the atmospheric pressure. As the change of the deflection of the top plate 101 is repeated in this manner, the corner edge portion 102a of the side wall 102 may be separated or rubbed off, as shown in FIG. 13, so that particles of aluminum which forms the side wall 102 inevitably scatter and contaminate the interior of the container.
As is generally known, semiconductor devices must be treated in a very clean atmosphere, so that their yield will be lowered if they are contaminated by the metal particles in the aforesaid manner.